This website contains affiliate links. As such, I will earn from qualifying purchases at no extra cost to you. This helps me maintain this website, so thanks in anticipation for your support.

Silicone rubber temperature resistance-for tents stove jacks

This post is about temperature measurement and temperature resistance of silicone rubber and composites of RTV silicone rubber that are glueable and sewable for making ultralight tent stove jacks.

The post reports on the ‘book values’ for temperature resistance of silicone rubber. It also reports on my empirically determined temperature resistance values for silicone rubber and my DIY cotton/RTV silicone rubber composite material. These temperature resistance values are discussed in relation to directly measured stove pipe temperatures along the length of an operational stove pipe.

Introduction to Silicone rubber temperature resistance

The reason

The reason for this post stems from my interest in using RTV silicone rubber on DIY outdoor adventure gear. It is a wonder material to a tinkerer like me. It has properties of; waterproofing, glueing, bonding, flexing, and heat-resisting. I have discussed these extensively in my posts; silnylon glueing, and DIY RTV silicone rubber uses, and DIY stove jack.

My innovative DIY stove jack is made with RTV silicone rubber. It protects my beautiful DIY ultralight tent from the heat from the stove pipe of my tiny and innovative DIY tent stove. Together these innovations enhance my enjoyment of winter ultralight backpacking and camping, preferably on skis. “I think you might get the picture.”

Kiss stove flue pipe exiting through the DIY stove jack that is glued and sewn to the tent after removing a previous pocket and metal gland tent protector.

Keeping it ultralight, simple, small and soft

Keeping the tent soft, light and stuffable is paramount for my backpacking. Consequently, I have rejected the traditional fibreglass and silicone flat stove jacks as being too heavy, stiff and clunky to go on my tents. “This argument is even stronger when using the tent with no intention of using the tent stove.” Instead, I have made alternative soft DIY stove jacks with RTV silicone rubber and fibrous composites materials made from it. Designing the stove jack to be safe at the peak stove pipe temperature is critical.

Cotton silicone DIY stove jack with cover flap open (~15g). When raised the flap forms a flashing gutter above the hole. "Yes. it does look like a 'dunny seat' that has been left up by the male of the house to torment the females of the house." — Cotton silicone DIY stove jack with cover flap open (~15g). When raised the flap forms a flashing gutter above the hole. “Yes. it does look like a ‘dunny seat’ that has been left up by the male of the house to torment the females of the house.”

Knowing a stove pipe’s top temperatures

For a good stove jack design, we must know the typical temperature and the peak temperature of the stove pipe surface where it contacts the stove jack.

For this post, I will be using my tiny DIY tent stove as the model for the testing of the temperature resistance of the silicone rubber and composites of the rubber. This stove is unlike the batch loaded stove described below. My test stove is:

Much smaller,
Has a skinny (37mm) stove pipe,
Is not batch loaded,
Maintains a balance of wood and charcoal fuel, and
The fuel sticks are fed in on an as-needed basis at a maximum rate of ~7g/minute and prevent fuel overload.

The tiny KISS tent stove mounted on wooden bush pole with a wood rack below. A tiny yet powerful stove that has an estimate 890 watt heat output from burning just 7g of sticks/minute. “That’s a joy to have in a winter tent and is similar to your regular household 1000 watt radiator.”

Most backpacking tent stoves are designed to be bach loaded with highly variable found wood fuels. Further combustion variability comes from the changes in the composition of the batch of wood within the stove. Without a constant and steady replenishment of the fuel, the fuel mix will change from; [much wood+much wood gas+minimal charcoal] into [predominantly charcoal+no wood+no wood gas). This means that they will have much more variable combustion behaviours and temperatures than my test stove that is continuously fed fuel sticks and maintains a balance between wood and charcoal fuels. I discuss these variable modes of wood combustion in detail in my post; wood and charcoal combustion.

Consequently, direct and accurate temperature measurement of stove pipe temperatures will be required for these stoves, rather than extrapolating from test results from my stove. Nevertheless, the temperature limits determined for the silicone materials will apply to any stove where the stoves stove pipe’s peak surface temperature can be measured or reasonable estimated.

Silicone rubber manufacture’s theoretical temperature resistance limits

The temperature limits (or book values) published by manufacturers makes a good starting point. Data from Shin-Etsu silicone indicate that the silicone contact point could be 150C indefinitely without causing significant damage. Even at 200C, it will last for 10,000h. “Now, that a lot of winter camping. Half-your-luck if you find time to wear out your stove jack.”

Also, according to Jebco an operating temperature could be 200-250C. Interestingly, they indicate that there is no melting point and that the autoignition point is around 450C.

I imagine this temperature could be reached on a large batch fed backpacking tent stove in a scenario where the stove is at the side of a tent and the pipe exit/stove jack contact point is low down on the stove pipe.
Me

They also indicate that during the combustion the silicone rubber produces a powdery white residue of silicon dioxide surface layer which slows oxygen supply to support the combustion. Consequently, if you should see white powder forming on your DIY ultralight stove jack you will know things are not quite right. Don’t breath that dust. Remember my silicosis warning.

I find it rather interesting that this rubber, which is made with much heat from harmless pure silicon dioxide sand, turns back into a deadly silicon dioxide powder when exposed to extreme heat.
Mothy The Elder

A new thermocouple is a wonderful and cheap stove tinkerer’s toy

The emperical temperature data in this post has been made possible by the acquisition of my first (cheap) thermocouple and meter package. It is a delightful instrument to use. It displaces the infrared thermometers that I have used for many years. The multiple limitations of these IR thermometers are described in another post titled; estimating ultralight stove temperature.

The thermocouple beats the hell out of my equally cheap infrared thermometers that I have used for tent stove temperature measurement for many years. For the first time, I can trust my high-temperature measurements of very hot and shiny metal stove surfaces.
Me

Thermocouple and infrared thermometer. The fused tip of the pair of thermocouple wires is shown above the meter. The thermocouple provides a much more accurate measurement of temperatures encountered on stove pipes.

Empirical temperature limit testing of silicone rubber materials

Lastly, throughout my life and career, I have always relished testing the ‘accepted norms’ by my own empirical testing. The tests in this post fit that paradigm. “In other words, suck-it-and-see. You never know what you will find out”.

Also, for my cotton fibre plus silicone composite that I use so much, it can only be empirically tested.

The combination of flammable cotton and silicone rubber is unlikely to be found in ‘book values’ of temperature resistance. It is about as likely as finding a published snowball survival time in the book of hell.
Mothy The Elder

These empirical tests and their practical implications constitute the major part of this post. They are, where possible, compared with ‘book values’ and finally validated with real-world stove field tests.

The measurement tools and testing rigs for silicone rubber temperature resistance testing

The IR thermometers have a convenient laser spot that shines where the temperature recording is to be taken from. “Pull the trigger and that’s your temperature held on the digital display without having to see or remember it while it is measured”. This makes the recording instant, direct, and easy but alas, seldom accurate for hot metal stove surfaces.

By contrast, the delicate fused bead of metal on the end of the fine thermocouple probe wires must be in contact with the hot stove surface for some seconds or dwell time to reach the true reading.

This dwell time increases with the temperature change that the sensor has sensed. Hovering the sensor bead in this way is ok for a quick single temperature measurement. However, it is not practical or effective for a series of measurements that need to be done on a hot stove surface that will inevitably have oscillating temperatures while finding the maximum.

Similar issues apply to the empirical testing temperature resistance of samples of silicone material. They must be held on or near the hot metal surface for a long time for effective testing. At the same time the metal surface must also have its temperature measured during the resistance testing.

My progression of test rigs inevitably became my solution to this challenge, but I will describe the progression of rigs. Apart from sharing my folly, the simple ones could be used for quick tests by others.

Rig 1- temperature testing

This first rig was designed to hold the thermocouple probe against the stove pipe within an insulated ring. I started my measurement down low on the hottest part of the flue system to do my first test. I ‘cranked up’ the stove, using fuel of thin fast-burning little sticks, (As shown in the photo below.). I recorded temperatures between 250-300C. “This was more variable than I expected given my claims of the steady flame that burns in this trickle feed test stove. The variation could be a lot more in a big batch fed stove.”

Thermocouple testing of flue pipe temperatures to determine the compatibility with a DIY ultralight stove jack.. — Thermocouple testing of flue pipe temperatures. The thermocouple wires are tucked inside a fine tube formed beside a thin stainless steel band that fits snuggly around the pipe. The thermocouple is held very close to the hot flue pipe surface (the hot guard/connector tube in this case). Successive layers of insulation around the ring ensure that there is little heat loss from the sensing zone. The sensor can make temperature measurements over any part of the formal flue pipe, where it would contact the DIY ultralight stove jack, by slipping the sensor housing up and down the pipe.

Next, I set this thermocouple holding rig at a height of about 1,800mm above the stovetop as this was near to where the flue pipe would exit the canopy, near the apex, on my pyramid tents. There I measured 103, 104, 110, 111, 114C and an aberrant 143C.

For years, when camping, I routinely stood up to do periodic ‘spit on the end of a finger tests’. By cautiously finding the lowest point at which stove pipe ‘spat back’. At this point, I assumed that I had found the 100C point on the pipe where water would boil and make a quiet zzzzt sound and a bubbly but not particularly hot feeding under my finger.

Caution: This test should only be done on a very thin foil stove pipe that has negligible thermal mass and only progressing from the low-temperature side to find the 100C zzzzt point.

It is time for an ode to my ancient the spit on the finger temperature test;

Multiple digital thermometers on both hands did sit,
Alas, for only two temperatures, were they fit,
For 100C to display or absolutely 373K,
Both reached just when steam from fingertip did spit.

Confirmation of this temperature high up on the stove pipe assured me of an ongoing very safe exit temperature with a very big safety margin where it passes through the stove jack.

This temperature test also indicated good stove draft, clean combustion, heating performance. It also ensures that the water in the invariably damp winter fuel sticks will exit the stove pipe as steam. Also, it meant that there would be no significant build-up of creosote, tar or soot in the roll up stove pipe when it comes time to pack up.

I was delighted that the above-measured temperatures concurred with my crude ‘100C spit test’ that I have trusted for many years. Importantly even the aberrant temperature measurement (143C) was not above the maximum safe protracted working temperature for silicone rubber (150-250 or even occasionally 300C as discussed above).

Rig 2- temperature resistance testing

I impatiently made a super simple handheld rig from some discarded medical forceps. “They make wonderful tinkerers tools.” I used them to hold a test sample of silicone composite fabric against a pen-nib shaped metal foil gauge.

The gauging tool was calibrated so that the fabric could be held at a fixed distance from the pipe by resting the tip against the pipe. Despite its simplicity, it worked, by holding the thermocouple steady nearby and reading the meter at the same time.

Cotton silicone temperature survival test probe for testing DIY stove jack materials. A curved stainless steel ‘pen-nib shaped’ probe has calibration lines marked on it, measure back from the tip. The test cloth can be spaced back from the tip according to the marks. This allows the fabric to be held at a fixed distance from the hot surface to test the survival according to the distance and temperature measured with the nearby thermocouple.

I ran out of time, but I did a short test with the embedded cotton set at 5mm from the pipe surface as shown in the above photo. I jumped right in and started at the hottest place, near the bottom of the stove pipe, (as shown in the photos above) with a temperature range of 230-300C. It showed no sign of damage. However, my hand was feeling quite uncomfortably hot and this was not a sustainable test rig for long term testing!

To me, the lack of damage done at this 5mm spacing was very encouraging and all options were open for this DIY low/hi-tech fabric made of shirt cotton and RTV silicone rubber. Almost as importantly, it inspired me to make the next stove pipe testing rig.

Rig 3- combined temperature and temperature-resistance testing

Rig 1. worked well enough. However, it was difficult to shift the rig up and down the stove pipe. I also realised that the insulating ring was unnecessary and may have inflated the real surface temperature.

My next step was to make an open thermocouple holder that also held a heat resistance testing rig (doing much the same as Rig 2.).

The rig was arranged so that the thermocouple bead just touched the hot surface without deforming the wires. The rig was placed on the hottest part of the flue pipe which was typically between 200-300C and the test piece of embedded cotton was held at 5mm from the stove pipe by an integrated spring clip. The test piece showed no signs of damage.

Thermal testing rig 3. It simultaneously measure temperatures and test for thermal decay in a sample of DIY stove jack material. It has a calibrated test bench with a spring clip that can hold the test fabric sample at various distances from the flue pipe (5mm in the photo). The test bench is located above the mounting ring that holds the rig to the flue pipe. The thermocouple temperature probe is just touching the flue pipe and is located below the mounting ring. The holding ring is loose fitting so that it can be easily moved up and down the pipe over the retaining rings. The asymmetric weighting of the load on the ring conveniently holds the rig in place. It also presses the probe and test bench gently against the pipe.

Rig 4- sustained high temperature-resistance testing

For sustained heat resistance testing, I thought that I could improve the test rig once more. Now that I could accurately measure temperature, I did not have to use the stove and use the position on a real stove pipe to guess the temperature.

I also thought that I could make the rig small so that it could be simply heated with my turbo ceramic candle. I hoped that it would not have temperature variations of a wood-burning stove.

For me, this would mean that I no longer had to climb ladders in the wind and rain to make my temperature measurements. I could do my testing in comfort in my house.
Me

Testing rig for exposing DIY stove jack fabrics samples to sustained high temperatures. The sample shown is silicone embedded cotton directly contacting the hot pipe (275C) of the test rig. The strip of foil on the top of the pipe was placed there to choke the airflow and raise the temperature a little. A more detailed photo of the damaged test strip is shown below. — Testing rig 4. for exposing DIY stove jack fabrics samples to sustained high temperatures. The sample shown is silicone embedded cotton directly contacting the hot pipe (275C) of the test rig. The strip of foil on the top of the pipe was placed there to choke the airflow and raise the temperature a little. A more detailed photo of the slight damage done to the test strip is shown below.

I was targeting a nice round figure of 300C for my first direct contact test but it only reached 290C. I put a sample of my cotton/silicone fabric and clipped it against the hot tube, mimicking what might be experienced by a DIY ultralight stove jack that was made entirely of this fabric.

There was some blackening of the end of the test strip, but it was still quite sound, flexible and clean to touch with no ‘telltale’ signs of white powdery silica from degraded silicone rubber. The progression of the blackening was limited to about 3mm (shown in photos below).

I speculate that the cotton fibres slowly charred when they reached about 96C (preventing laundromat fires). Eventually, the temperature beyond the 3mm band was not hot enough for charring. The blockage of the air entry path with charr residue may have provided some oxidization protection. Either way, the damage seems inconsequential and only a little unsightly.

Cotton shirt fabric samples for DIY stove jacks after thermal testing. Silicone/cotton finishing in a 10mm wide band of pure silicone (left, front, maximum temperature ~275C). Silicone/cotton only (left, front, maximum temperature ~290C ). There was no visible damage to the test strip that finished in pure silicone and only cosmetic charing of the cotton within the tip as well as slight curling with the silicone/cotton only sample. There was so sign of that deadly white silicon dioxide powder that can cause silicosis. — Cotton shirt fabric samples for DIY stove jacks after thermal testing. Silicone/cotton finishing in a 10mm wide band of pure silicone (left, front, maximum temperature ~275C). Silicone/cotton only (left, front, maximum temperature ~290C ). There was no visible damage to the test strip that finished in pure silicone and only cosmetic charing of the cotton within the tip as well as slight curling with the silicone/cotton only sample. There was no sign of that deadly white silicon dioxide powder that can cause silicosis.

Here is a little video of rig 4. in action where the temperature reached ~320C. The temperature was higher for some unknown reason than in earlier tests. Howerer, was much more stable and predictable than temperatures on the pipe of a wood-fired tent stove.

View this post on Instagram

A post shared by Tim Clarke (@telemarktim)

Conclusion about silicone rubber temperature resistance

The DIY composite cotton/silicone rubber stove jack fabric survived sustained contact with a 300C surface. The embedded cotton fibre charred for about 3mm in from the contact line, but left the silicone intact with a small amount of curving. The softness and curvature after heating would not make the fabric a suitable stand-alone stove jack that would shed snow and water and withstand the buffeting of storms and strong wind.

When a simple10mm boundary layer of RTV silicone rubber was added to the cotton/silicone sheet it survived sustained contact at 275C (and theoretically should survive 300C) without any visible deterioration.

If the cotton/silicone fabric is used as a soft glueable and sewable interface with the tent, it can have a small (10mm wide*3mm thick) boundary layer of RTV silicone rubber custom moulded and bonded to fit closely around the stove pipe (as shown below).

Embedded cotton DIY stove jack with an additional heat resistant boundary layer of pure silicone rubber. The silicone/cotton composite is delightfully easy to sew (by machine or hand stitching) after glueing to the tent.

With this extra silicone boundary layer, the stove jack should leave the tent soft and stuffable for ultralight backpackpacking. It should hold the stove pipe stable in wind storms and be able to survive a sustained stove pipe contact temperature of 300C.

This maximum temperature should never be reached on the upper reaches, of my tiny KISS tent stove with a highly regulated fuel feed rate. It would seldom reach 300C at the bottom of the stove pipe.

I suppose this means that my stove pipe could have an exit at any reasonable height without breaching the 300C limit. However, I see no good reason to shift my stove pipe from favourite one that is close to the middle of my tent.
Me

Kiss stove flue pipe exiting through the DIY stove jack that is glued and sewn to the tent. — Kiss stove flue pipe exiting through the DIY stove jack that is glued and sewn to the tent after removing a previous pocket and metal gland tent protector.

For the large batch fed tent stoves (as discussed earlier) temperatures above 300C may be encountered, particularly if the stove pipe exits through the tent canopy at a lower level on the stove pipe.

In this case, an additional cylindrical metal foil shield tube could be added. An example that used the foil from a soft drink can is shown below. This

DIY ultralight stove jack protective sleeve. — DIY ultralight stove jack protective sleeve that is made from a soft drink can.

DIY ultralight stove jack protective sleeve viewed from outside.

Tim

Ultralight Backpacking Gear

Silicone rubber temperature resistance- for tents stove jacks